function ajax(opt) {
	opt = opt || {};
	opt.method = opt.method.toUpperCase() || 'POST';
	opt.url = opt.url || '';
	opt.async = opt.async || true;
	opt.data = opt.data || null;
	opt.success = opt.success || function() {
	};
	var xmlHttp = null;
	if (XMLHttpRequest) {
		xmlHttp = new XMLHttpRequest();
	} else {
		xmlHttp = new ActiveXObject('Microsoft.XMLHTTP');
	}
	var params = [];
	for ( var key in opt.data) {
		params.push(key + '=' + opt.data[key]);
	}
	var postData = params.join('&');
	if (opt.method.toUpperCase() === 'POST') {
		xmlHttp.open(opt.method, opt.url, opt.async);
		xmlHttp.setRequestHeader('Content-Type',
				'application/x-www-form-urlencoded;charset=utf-8');
		xmlHttp.send(postData);
	} else if (opt.method.toUpperCase() === 'GET') {
		xmlHttp.open(opt.method, opt.url + '?' + postData, opt.async);
		xmlHttp.send(null);
	}
	xmlHttp.onreadystatechange = function() {
		if (xmlHttp.readyState == 4 && xmlHttp.status == 200) {
			opt.success(xmlHttp.responseText);
		}
	};
}